To review your peers' papers just click on one of the paper types on the left and read through a submission. When you are done click on EDIT on the right of the screen. This will bring you to an editing page. Here, you can add suggestions, ask questions that needs to be answered, offer your opinion, fix formatting problems, etc... all the things we do during peer review in class. To make sure that the person notices it, look above - there is a T on top of a colorful globe. Click on this - you will see that you can change the font, the color, the size.

Hint - Do NOT hit ENTER. It deletes stuff - it just deleted this and I am typing it again!!
Also - it is much easier to type whatever you want to say and then block it and click on the little T with the globe, AFTER you have written it. Some glitch with the program makes it hard to change before typing.